Clinical activity of anti-Gram-positive agents against methicillin-resistant Staphylococcus aureus

Current concerns about multiresistance and a diminishing antibiotic pipeline are mainly addressed to Gram-negative bacteria. The greatest fear within the Gram-positive arena is vancomycin-resistant Staphylococcus aureus. Its epidemiology and clinical presentation give cause for concern, but so far its impact has been strictly limited. While this may change, the loss of glycopeptides as a treatment option may not, in fact, be all bad news.     

Comparative in vitro activity of coumermycin against methicillin-resistant Staphylococcus aureus.

Coumermycin was the most active agent in vitro against methicillin-resistant Staphylococcus aureus when compared with fusidic acid, imipenem, rifampin, trimethoprim-sulfamethoxazole, and vancomycin. The MICs of coumermycin ranged from 0.002 to greater than 4 micrograms/ml and from 0.5 to greater than 4 micrograms/ml for inocula of 10(4) and 10(6) CFU/ml, respectively. The combination of coumermycin with either cephalothin or ciprofloxacin showed some synergy; antagonism was found with gentamicin.     

Bactericidal activity of orally available agents against methicillin-resistant Staphylococcus aureus

BACKGROUND: The recent proliferation of community-acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) has led to a marked increase in the need for outpatient treatment of MRSA infections. Many oral agents active against MRSA have been available for years, and a paucity of literature compares them, leaving physicians with little guidance for choosing among them. The purpose of the present study was to compare the bactericidal effects of orally available antibiotics against MRSA and to determine whether there were differences in antimicrobial killing activity against CA-MRSA and hospital-acquired (HA) MRSA isolates. METHODS: A total of 12 unique patient MRSA isolates were studied. Six strains were CA, carrying the staphylococcal chromosomal cassette (SCCmec) type IVa, while six were HA and carried SCCmec type II. Time-kill methods were used to study the bactericidal activity of the orally available antimicrobials linezolid, rifampicin, trimethoprim/sulfamethoxazole, clindamycin, minocycline, and moxifloxacin alone and in combination in vitro. RESULTS: Trimethoprim/sulfamethoxazole was rapidly bactericidal resulting in >2 log(10) cfu/mL decrease at 8 h and >3 log(10) cfu/mL decrease at 24 h in vitro. No antibiotic combination exhibited better killing than trimethoprim/sulfamethoxazole alone. Adding rifampicin to trimethoprim/sulfamethoxazole showed a trend towards antagonism in vitro. There were no differences in the bactericidal activity of any antimicrobial or antimicrobial combination against MRSA isolates carrying SCCmec type IVa versus those carrying SCCmec type II. CONCLUSION: Trimethoprim/sulfamethoxazole is rapidly bactericidal against MRSA in vitro when compared with most other orally available antimicrobials. No differences in bactericidal activity were detected when activities against CA-MRSA and HA-MRSA were compared.     

利奈唑胺、替加环素、达托霉素、头孢吡普等抗菌药物对MRSA的抗菌活性

目的多中心研究我国2005年MRSA的耐药现状，评价利奈唑胺、替加环素、达托霉素和头孢吡普等药物的抗菌活性。方法收集2005年1月至2005年12月14个地区连续分离的非重复金葡菌809株，采用琼脂稀释法测定抗菌药物的MIC。结果MRSA发生率为50．3％，其中MRSA发生率最高的为大连（93．3％）、上海（80．3％），其次为南宁（63．6％）、北京（55．5％）、青岛（53．8％）。MRSA对红霉素的敏感性为4．2％，喹诺酮类药物为4．4％～12．6％，庆大霉素为9．6％，四环素为11．1％，对MRSA活性较高的有氯霉素（82．3％）和复方磺胺甲嗯唑（78．6％）；MRSA对替考拉宁、万古霉素、利奈唑胺、替加环素、达托霉素和头孢吡普均全部敏感。头孢吡普、达托霉素、替加环素、利奈唑胺的MIC50和MIC90分别为2，2mg／L；0．5，0．5mg／L；0．125，0．25mg／L；1，2mg／L。MIC范围分别为0．125～2mg／L，0．125～1mg／L,0.064～0．5mg／L，0．25～2mg／L。结论我国MRSA发生率高，多重耐药严重，不同地区MRSA发生率有所差异，头孢吡普、达托霉素、替加环素和利奈唑胺对于MRSA具有很高的抗菌活性。     

The in-vitro activity of some antimicrobial agents against methicillin-resistant Staphylococcus aureus

A total of 185 strains of methicillin resistant Staphylococcus aureus was investigated for sensitivity to five other antimicrobial agents. The vast majority of these strains were also resistant to gentamicin and fusidic acid. Rifampicin was the most active drug tested (MIC90, 0.007 mg/l), while two newer compounds teichomycin and ciprofloxacin showed equal and appreciable activity (MIC90, 0.5 mg/l).     

In vitro activity of linezolid against vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae.

We report the activity of the new oxazolidinone antimicrobial agent linezolid against 37 clinical isolates of vancomycin-resistant enterococci (including organisms carrying the vanA, vanB, vanC-1, and vanC-2/3 genes), 26 clinical isolates of methicillin-resistant S. aureus and 20 clinical isolates of high-level penicillin-resistant S. pneumoniae. All isolates of vancomycin-resistant enterococci were inhibited by < or = 4 ug/ml of linezolid. All isolates of methicillin-resistant S. aureus were inhibited by < or = 8 ug/ml of linezolid. All isolates of penicillin-resistant S. pneumoniae were inhibited by < or = 2 ug/ml of linezolid. Linezolid inhibits strains of multidrug resistant Gram-positive cocci in vitro at concentrations < or = 8 ug/ml.     

In vitro susceptibility of methicillin-resistant Staphylococcus aureus and slime-producing and non-slime-producing coagulase-negative staphylococci to fusidic acid.

The in vitro susceptibility of 100 oxacillin-resistant Staphylococcus aureus and 100 oxacillin-resistant coagulase-negative staphylococci (CNS; 50 slime-negative and 50 slime-positive strains) was determined by agar dilution technique, with and without the addition of 50% human serum. All strains tested were highly sensitive to fusidic acid. S. aureus and CNS showed MIC50 values of 0.125 and 0.25 mg/l, respectively. MICs of all strains increased significantly in the presence of 50% human serum. Only minor differences were noted between the MICs of slime-producing and slime-deficient CNS.     

Comparative activity of telavancin against isolates of community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES: This study compared the activity of telavancin, a novel multivalent lipoglycopeptide with rapid bactericidal activity, with those of five standard antibiotics for methicillin-resistant Staphylococcus aureus (MRSA) against isolates of community-associated MRSA (CA-MRSA). METHODS: Microdilution tests performed according to CLSI guidelines using cation-adjusted Mueller-Hinton broth were used to determine the MIC values of telavancin, quinupristin/dalfopristin, vancomycin, trimethoprim/sulfamethoxazole, linezolid and daptomycin versus 60 CA-MRSA isolates. MBC values of telavancin were determined according to CLSI guidelines and American Society for Microbiology standards. PFGE was performed using the restriction enzyme SmaI. Samples from three predominant pulsed-field types were typed by multilocus sequence typing. Staphylococcal cassette chromosome mec typing was determined by multiplex PCR. The Panton-Valentine leucocidin (PVL) genes (lukS-PV and lukF-PV) were identified by PCR. RESULTS: The telavancin MIC90 and MBC90 values for this collection of 60 CA-MRSA isolates were 0.5 and 1 mg/L, respectively, with MIC and MBC values both ranging from 0.25 to 1 mg/L. Telavancin was found to be bactericidal in this study, as its MBC was no more than 2-fold higher than its MIC for all CA-MRSA isolates tested except one. (A single isolate yielded an MBC/MIC ratio of 4.) PVL- and non-PVL-producing strains demonstrated similar susceptibility to telavancin and comparator agents. CONCLUSIONS: Based on in vitro activity, telavancin should be an effective agent against CA-MRSA.     

In vitro and in vivo activity of coumermycin and other antibacterial agents against methicillin-resistant strains of Staphylococcus aureus

The in vitro activity of coumermycin, fusidic acid, cotrimoxazole, and vancomycin was determined by broth microdilution assay against 33 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates from the Detroit Receiving Hospital, Detroit, Mich. Coumermycin was the most active drug tested, while fusidic acid, vancomycin, and cotrimoxazole also had good activity. The four antimicrobials were tested in vivo against 7 strains of MRSA employing the mouse protection model. Again, coumermycin was the most active, followed by vancomycin, cotrimoxazole, and fusidic acid. Coumermycin was very active, while vancomycin and fusidic acid were inactive in neutropenic mice infected with an MRSA strain. Coumermycin retained activity when given 18 h before an MRSA infection, while vancomycin activity was lost. Coumermycin was active in a local thigh infection while vancomycin was inactive. The results indicate that coumermycin is potent against MRSA with activity equal or superior to comparable agents in various experimental mouse infections.     

In vitro activity of N-formimidoyl thienamycin and other beta-lactam antibiotics against methicillin-resistant Staphylococcus aureus.

Of 43 isolates of methicillin-resistant Staphylococcus aureus, 90% were inhibited by 8 micrograms or less of N-formimidoyl thienamycin per ml by the agar-dilution technique. Cefamandole, cefotaxime, cefoperazone, moxalactam, and cefsulodin showed relatively poor activity. Vancomycin was the most active compound by weight, inhibiting 93% of strains at 1 microgram/ml.     

利奈唑胺和万古霉素治疗甲氧西林耐药金黄色葡萄球菌感染的疗效比较

甲氧西林耐药金葡菌(MRSA)感染可选择的治疗药物有限,多年来万古霉素是治疗的金标准。对万古霉素敏感性下降菌株的出现,增加了对新型抗感染药物的需求,噁唑烷酮类药物利奈唑胺是治疗MRSA感染的新药。然而,评价该药临床疗效的研究较少。本文比较利奈唑胺与万古霉素治     

In-vitro activity of coumermycin against methicillin-resistant staphylococci: a comparison with six other agents

The in-vitro activity of coumermycin was compared with that of vancomycin, rifampicin, fusidic acid, trimethoprim-sulphamethoxazole, norfloxacin and cefamandole against seven isolates of methicillin-resistant Staphylococcus aureus and 97 isolates of methicillin-resistant coagulase negative staphylococci. Apart from one strain of methicillin-resistant S. aureus all isolates were inhibited by less than or equal to 0.06 mg/l of coumermycin. Cefamandole was more active against strains of S. epidermidis than against other coagulase negative staphylococci.     

Development of a rapid diagnostic assay for methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative Staphylococcus

We describe here a rapid assay for the detection of the tuf gene for the identification of Staphylococcus genus, the femB gene for the identification of Staphylococcus aureus species, and the mecA gene for the identification of methicillin resistance directly from BACTEC blood culture bottles showing Gram-positive cocci in clusters. The test, configured on a thin-film biosensor platform, allows for detection of genomic DNA from blood culture samples without the need for nucleic acid amplification. In an initial study to validate the technology, 107 consecutive positive blood cultures were tested on the thin-film biosensor, and the assay exhibited 100% concordance in comparison with standard microbiological methods for identifying methicillin-susceptible and methicillin-resistant S. aureus and for identifying methicillin-susceptible and methicillin-resistant coagulase-negative Staphylococcus. Results were obtained within 90 min directly from signal positive bottles with no instrumentation required.     

In vitro activities of arylomycin natural-product antibiotics against Staphylococcus epidermidis and other coagulase-negative staphylococci

The arylomycins are a class of natural-product antibiotics that act via the inhibition of type I signal peptidase (SPase), and we have found in diverse bacteria that their activity is limited by the presence of a resistance-conferring Pro residue in SPase that reduces inhibitor binding. We have also demonstrated that Staphylococcus epidermidis, which lacks this Pro residue, is extremely susceptible to the arylomycins. Here, to further explore the potential utility of the arylomycins, we report an analysis of the activity of a synthetic arylomycin derivative, arylomycin C₁₆, against clinical isolates of S. epidermidis and other coagulase-negative staphylococci (CoNS) from distinct geographical locations. Against many important species of CoNS, including S. epidermidis, S. haemolyticus, S. lugdunensis, and S. hominis, we find that arylomycin C₁₆ exhibits activity equal to or greater than that of vancomycin, the antibiotic most commonly used to treat CoNS infections. While the susceptibility was generally correlated with the absence of the previously identified Pro residue, several cases were identified where additional factors also appear to contribute.The coagulase-negative staphylococci (CoNS) are a heterogeneous group of at least 15 different species of Gram-positive bacteria that have emerged in recent decades as important nosocomial pathogens (10, 31). A particularly problematic species is Staphylococcus epidermidis, which is responsible for a growing number of infections among hospital patients with compromised immune systems and is especially notorious for forming biofilms that adhere to surgical equipment and other hospital surfaces and indwelling devices (3, 18). Methicillin was traditionally the first-line antibiotic against CoNS, but its widespread use has resulted in resistance in 50% to 80% of CoNS infections and 75 to 90% of nosocomial S. epidermidis infections (18). As a result, vancomycin is now the first line agent for treating CoNS infections; however, isolates with reduced susceptibility to vancomycin have also been observed (11, 26), and the emergence of enterococci harboring mobile elements that confer vancomycin resistance has raised concerns that resistance might be transferred to S. epidermidis and/or other CoNS (17, 28). These concerns continue to motivate the search for new antibiotics that are active against CoNS, especially S. epidermidis.The arylomycins (Fig. ​(Fig.1)1) are a novel class of natural-product antibiotics that act by inhibiting bacterial type I signal peptidase (SPase) (19, 25). SPase is a Ser-Lys dyad protease that removes N-terminal signal sequences from preproteins following their translocation across the cytoplasmic membrane (5, 20). SPase is an attractive target for antibiotic therapy because it is conserved, essential, and located in the relatively accessible outer leaflet of the cytoplasmic membrane. Furthermore, because bacterial SPase acts via a catalytic mechanism that is distinct from that of its eukaryotic homologues, the arylomycins are unlikely to exhibit mechanistic toxicity in humans (5, 20).Open in a separate windowFIG. 1.Structures of arylomycin A₂ (R = iso-C₁₂) and arylomycin C₁₆ (R = iso-C₁₆) [iso-C₁₂ = CH₂(CH₂)₇CH(CH₃)₂ and iso-C₁₆ = CH₂(CH₂)₁₁CH(CH₃)₂].Despite the apparent accessibility, essentiality, and conservation of SPase, initial reports suggested that the arylomycins were active against only a few Gram-positive bacteria, including Streptococcus pneumoniae, Rhodococcus opacus, and Brevibacillus brevis (15, 25), and not against other important Gram-positive pathogens or against any Gram-negative bacteria. However, after reporting the first synthesis of an arylomycin, arylomycin A₂, as well as the synthetic derivative arylomycin C₁₆ (Fig. ​(Fig.1),1), we found that each potently inhibits the growth of S. epidermidis (24) and that S. epidermidis evolves resistance to the arylomycins by mutating residue 29 of one of its two SPases, SpsIB, from Ser (Ser²⁹) to Pro (Pro²⁹) (29). Moreover, a Pro residue is naturally present at the analogous position in the homologous SPases of the pathogens Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and we showed that it imparts resistance by reducing the affinity with which the arylomycins bind. Furthermore, we found that a remarkably diverse range of both Gram-positive and Gram-negative bacteria whose SPases lack a Pro at the analogous position are susceptible to the arylomycins, including Staphylococcus epidermidis, Streptococcus pyogenes, Helicobacter pylori, Chlamydia trachomatis, and some strains of Francisella tularensis (29). In total, the results suggest that the identified SPase polymorphism is a major contributor to naturally occurring arylomycin resistance. However, we also showed that Yersinia pestis and some strains of S. aureus are susceptible to the arylomycins despite the presence of an analogous Pro, while others, such as many of the Lactobacillales, Clostridia, and Bacteriodetes, are resistant despite its absence, implying that in some cases, susceptibility must depend on additional factors, such as variable levels of toxicity associated with the inhibition of protein secretion.The potent activity of the arylomycins against a strain of S. epidermidis (RP62A) suggests that they might be useful in the treatment of this and perhaps other CoNS. Here, to examine the spectrum of activity of the arylomycins against clinical isolates of S. epidermidis and other CoNS, we report the activity of arylomycin C₁₆ against two panels of isolates from hospitals in geographically diverse locations and compare the activity to that of vancomycin. The results reveal that the arylomycins have potent antibacterial activity against a range of important CoNS species whose SpsIB orthologs lack the previously identified resistance-conferring Pro, while less activity is observed against species where Pro is present. While we generally observed similar susceptibilities for different isolates within a species, significant differences were observed in several cases, with one atypical instance of susceptibility resulting from the presence of a Ser in place of the resistance-conferring Pro. Significant differences in susceptibility between isolates of the same species are usually observed with clinically deployed antibiotics where selection for resistance has occurred during therapy (2, 9, 14, 21), and therefore, these results may be relevant to understanding the natural evolution of arylomycin resistance in nature.     

In vitro activity of ceftobiprole, linezolid, tigecycline, and 23 other antimicrobial agents against Staphylococcus aureus isolates in China

We investigated the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in China and determined the susceptibility of S. aureus to 26 antimicrobial agents, including ceftobiprole, linezolid, and tigecycline. A total of 798 isolates were collected and tested by agar dilution. The mean prevalence of MRSA was 50.4%, the highest in Shanghai (80.3%), followed by those in Beijing (55.5%) and Shenyang (50.0%). Only 4.2% to 12.6% of MRSA were susceptible to erythromycin, fluoroquinolones, gentamicin, and tetracycline. All isolates were susceptible to teicoplanin, vancomycin, linezolid, tigecycline, and ceftobiprole.     

In vitro activity of pristinamycin against methicillin-resistant Staphylococcus aureus

An agar dilution technique was used to determine the MIC of pristinamycin for 124 clinical isolates of methicillin-resistant Staphylococcus aureus. All were inhibited by less than or equal to 0.5 mg/1, quite similar to the sensitivity of a number of methicillin-sensitive strains. MICs obtained using a microdilution method were also comparable. Antagonism was seen with the combination of pristinamycin and erythromycin.     

Identification of methicillin-resistant isolates of Staphylococcus aureus and coagulase-negative staphylococci responsible for bloodstream infections with the Phoenix system

We evaluated the reliability of the new Phoenix system (Becton Dickinson Microbiology Systems, Sparks, Md.) in species-level identification and detection of oxacillin (methicillin) resistance among 493 staphylococcal isolates (Staphylococcus aureus, n = 223; coagulase-negative staphylococci, CoNS, n = 270) recovered from patients with bacteremia. Identification results were concordant with those of the ID 32 STAPH system (bioMérieux, Marcy l'Etoile, France) for 100% of S. aureus (223/223) and 97.4% (263/270) of CoNS isolates. For S. aureus isolates, Phoenix oxacillin-susceptibility results fully concurred with those of mecA polymerase chain reaction (PCR) (reference method): 96 mecA-positive isolates identified as resistant, 127 mecA-negative strains as susceptible. Two of the 210 mecA-positive CoNS isolates were misclassified as susceptible by the Phoenix (sensitivity 99%, positive predictive value 97.6%). Five of 60 mecA-negative CoNS isolates were classified as resistant by the Phoenix (specificity 91.7%; negative predictive value 96.5%). The Phoenix system can provide accurate and reliable identification of methicillin-resistant staphylococci responsible for bloodstream infections.